The present invention generally relates to magnetic information storage devices and more particularly to a magnetic information storage device for recording and reproducing an information signal on and from a rigid magnetic disk that is revolved at a high speed in a hermetically sealed environment.
In the magnetic information storage devices of the so-called hard disk, a rigid magnetic disk revolving at a high speed such as several thousand r.p.m. is used for a recording medium, and recording and reproduction of information signals are achieved on and from the magnetic disk by means of a magnetic head that scans the surface of the magnetic disk without establishing contact therewith. The conventional hard disk device having a construction as such generally provides a very high access speed in the order of ten milliseconds or less and is used extensively as the auxiliary storage devices of computers and microprocessors. On the other hand, the conventional hard disk device occupies a considerable space mainly due to the size of the floating magnetic head and the space in which the magnetic head moves, and there exists a substantial difficulty in the reduction in the size of the device. Further, such a conventional hard disk device that uses a floating magnetic head is vulnerable to external shock.
On the other hand, there is proposed a new type of hard disk device that uses a very small, needle-like magnetic head that contacts with the surface of the revolving magnetic disk as shown in FIG. 1.
Referring to FIG. 1, the hard disk device is constructed on a base body 10 that defines a hermetically sealed space therein together with another base body part not illustrated. In the hermetically sealed space formed as such, there is provided a chassis 11 on which a shaft 12 is fixed. Further, the chassis 11 carries thereon a motor not illustrated in FIG. 1 and the motor drives a stage 13a such that the stage 13a revolves about the shaft 12 at a high speed typically in the order of several thousand r.p.m.
The stage 13a thus driven by the motor carries thereon one or more magnetic disks 13 wherein the magnetic disk 13 is formed of a rigid material such as aluminum and carries a magnetic coating. Further, a magnetic head assembly 14 is provided on the base body 10, wherein the magnetic head assembly 14 includes a shaft 16 that is fixed on the base body 10, and an arm 15 is mounted on the shaft 16 such that the arm 15 swings freely about the shaft 16. The arm 15 carries at a free end thereof a needle-like magnetic head member 17 that is urged to establish a continuous contact to the surface of the disk 13, typically with an urging force of about 0.5 mN, corresponding to a magnetic head of about 1 mg in mass. Further, the arm 15 is driven by an electromagnetic actuator 18 provided on the base body 10, and the needle-like magnetic head member 17 at the free end of the arm 15 scans the surface of the magnetic disk 13 in a radial direction thereof in response to the swinging motion of the arm 15.
It should be noted that the magnetic head member 17 carries a magnetic head at a tip end thereof, and the information signal picked up at the magnetic head part is transferred to a terminal pad 20 on the base body 10 via a flexible cable 19. Further, the flexible cable is used for supplying an electric power for actuating the arm 15. When recording information, on the other hand, the information signal is supplied to the magnetic head part from the terminal pad 20 via the flexible cable 19 for causing a magnetization of the magnetic disk 13 in response to the information signal.
FIG. 2 shows the arm 15 and the magnetic head member 17 attached thereto in more detail, wherein the arm 15 is formed of a resilient material such as aluminum and the magnetic head member 17 is attached to the arm 15 by an adhesive. Further, it will be noted that the arm 15 is formed with a U-shaped part in correspondence to a part that is mounted on the magnetic head assembly 14.
FIG. 3 shows the arm 15 and the head member 17 of FIG. 2 in the assembled state, wherein the arm 15 is mounted on a rotary sleeve 14a that in turn is fitted upon the shaft 16 shown in FIG. 1 such that the sleeve 14a can rotate freely about the shaft 16. The sleeve 14a carries a frame 14b that in turn carries a coil thereon, and the coil on the frame 14b is driven, with respect to a stator in the electromagnetic actuator 18, in response to a drive current that is supplied via the flexible flat cable 19. Thereby, the arm 15 experiences a swinging motion in response to the energization of the actuator 18.
FIG. 4 shows the cross sectional view of the hard disk device of FIG. 1, wherein only essential part will be described.
Referring to FIG. 4, it will be noted that the base body 10 carries a motor M such that the motor M surrounds the shaft 12, and a rotor 13a is provided to surround the motor M. There, the rotor 13a is held rotatable about the shaft 12 by a bearing 13b and is driven upon energization of the motor M. The magnetic disk 13 is fixed upon the rotor 13a and revolves unitarily with the rotor 13a about the shaft 12. In the illustrated example, two magnetic disks are provided parallel about the common shaft 12. Further, it will be understood that the sleeve 14a is held rotatable about the shaft 16 by a bearing 14c. The electromagnetic actuator 18 includes stator magnets that are disposed above and below the frame 14b.
In FIG. 4, it is important to note that the needle-like magnetic head member 17 establishes a contact engagement with the surface of the magnetic disk 13. As already mentioned, the arm 15 resiliently urges the head member 17 upon the magnetic disk 13, and the recording and reproduction of information signals is achieved in the state that the head member 17 maintains the contact engagement with the surface of the revolving magnetic disk 13. By using the needle-like magnetic head member 17, one can reduce the space occupied by the magnetic head in the hard disk device, and the number of the magnetic disks that are mounted on the common shaft can be increased. Alternatively, one can reduce the height of the hard disk device. The components of the disk drive are covered by a cover lid 21.
FIG. 5 shows the overall view of the magnetic head member 17 in a slightly enlarged scale.
Referring to FIG. 5, it will be noted that the magnetic head member 17 includes a resilient main body 17a having a first end 17b in which a magnetic head is formed and a second, opposite end 17c that is adapted for mounting on the arm 15. The magnetic head of FIG. 5 is described in the U.S. Pat. No. 5,041,932 to Hamilton, which is incorporated herein as reference.
FIG. 6 shows the magnetic head that is formed in the end part 17b of the magnetic head member 17 in an enlarged cross section.
Referring to FIG. 6, the magnetic head member 17 is defined with a slide surface 17h between an end surface 17j and a bottom surface 17i for contact engagement with the magnetic disk 13, and a magnetic yoke 17d is embedded in the magnetic head member 17 together with a coil 17e. The lead coil 17e is connected to a lead wire 17g. Further, the magnetic yoke 17d forms a gap 17f in correspondence to the slide surface 17h for creating a magnetic field that penetrates into the magnetic disk 13.
FIGS. 7(A) and 7(B) show the state of engagement of the magnetic head member 17 and the magnetic disk 13, wherein FIG. 7(A) shows the normal contacting state while FIG. 7(B) shows the abnormal state. In the state of FIG. 7(A), the angle of the magnetic head member 17 with respect to the magnetic disk 13 is optimized such .that the slide surface 17h establishes the desired contact engagement with the magnetic disk 13 with an optimized pressure. On the other hand, when the angle is inappropriate as shown in FIG. 7(B), the slide surface 17h fails to contact with the disk 13 and the recording and reproduction characteristics of information signals become deteriorated substantially. As the magnetic head member 17 is mounted on the arm 15 by an adhesive or laser welding, the adjustment of the contact angle of the head member 17 is generally impossible in the magnetic head assembly 14 of the conventional type. Thereby, the assembling process has to be conducted extremely precisely and the yield of the product deteriorates accordingly.